Porous polymeric particles have been prepared and used for many different purposes. For example, porous particles have been described for use in chromatographic columns, ion exchange and adsorption resins, drug delivery devices, cosmetic formulations, papers, and paints. The methods for generating pores in polymeric particles are well known in the field of polymer science. However, each particular porous particle often requires unique methods for their manufacture. Some methods of manufacture produce large particles without any control of the pore size while other manufacturing methods control the pore size without controlling the overall particle size and particle size distribution.
U.S. Pat. No. 3,957,741 (Rembaum et al.) describes crosslinked acrylate porous polymer particles having an average size less than 2 μm and various functional groups incorporated in the polymer.
U.S. Pat. No. 4,775,699 (Cozens) describes skinless porous polyvinyl chloride (PVC) particles having greater than 20% of the surface area made up of PVC and a particle size greater than 70 μm.
U.S. Pat. No. 6,780,942 (Leon et al.) describes porous particles prepared from various polyesters, which particles have pores in the outer surfaces.
In the publication by C. M. Cheng, J. W. Vanderhoff, and M. S. El-Aasser, J. Polym. Sci.: Part A, Polymer Chemistry, Vol. 30, pp. 245-256, 1992, the authors described porous particles having a pore size less than 100 nm and a particle size of 10 μm that are swellable in organic solvents.
Marker material can be included in porous particles so that the particles can be detected for a specific purpose. For example, U.S. Patent Application Publications 2008/0176157 (Nair et al.) and 2010/0021838 (Putnam et al.) and U.S. Pat. No. 7,754,409 (Nair et al.) describe porous particles and a method for their manufacture, which porous particles are designed to be toner particles for use in electrophotography. Such porous particles typically contain a colorant such as carbon black or another pigment to provide desired black-and-white or color electrophotographic images. Such porous particles (“toners”) can be prepared using a multiple emulsion process in combination with a suspension process (such as “evaporative limited coalescence”, ELC) in a reproducible manner and with a narrow particle size distribution.
Still another important use of polymeric particles is as a means for marking documents, clothing, or labels as a “security” tag. For example, U.S. Pat. No. 5,385,803 (Duff et al.) describes a process of authentication of documents using an electrophotographic process and core-shell toner particles containing an infrared emitting component and a detection step. U.S. Patent Application Publication 2003/0002029 (Dukler et al.) describes a method for labeling documents for authentication using a toner particle containing two or more mixed compounds having a characteristic detectable signal.
Product counterfeiting occurs in artworks, CD's, DVD's, computer software recorded on various media, perfumes, designer clothes, handbags, luggage, automobile and airplane parts, securities (for example stock certificates), identification cards (for example, drivers' licenses, passports, visas, and green cards), credit and debit cards, smart cards, and pharmaceuticals. The application of a security marker or taggant to an object or product for authenticating the origin or intended market is known in the art. Security markers can be incorporated into components that make up the object or product, or they can be incorporated into papers, inks, or varnishes that are applied to the object or product, or they can be incorporated into labels affixed to the object, product, or packaging there for. The presence of the security marker can be used to verify the authenticity of the origin of the object using suitable detection means that is specific to the security marker.
Some systems used for detecting the security markers are often known as “forensic” systems because they tend to require sophisticated equipment (for example high power microscopes) in a laboratory analysis. Other detection systems are designed for “field” use and are known as “covert” systems as they can be used outside the laboratory with specially designed equipment for the specific security markers being detected.
Some security markers can be dispersed within a carrier varnish and are referred to as particle-based or pigment-based markers. Such markers remain intact in the varnish and will appear as particles when examined microscopically. Other security markers are dissolvable in an ink or varnish and distributed in the carrier on a molecular level. These markers are not readily detected with a microscope and require more sophisticated detection equipment.
A means for detecting a population of microparticles is described in U.S. Pat. No. 5,450,190 (Schwartz et al.). Groups of microparticles of specific sizes and fluorescent properties or colors are mixed with toner particles and the resulting mixture is used in laser printer cartridges or photocopy machines to provide detectable images.
Particles having two or more different light emitting species can also be printed onto various substrates using various printing means, as described in WO 2007/051035 (Haushalter).
Toner particles having a luminescent material that includes quantum dots are described in EP 2,025,525 (Wosnick et al.) and can be used to form detectable markings on substrates. These toner particles can also include colorants or other detectable components.
Copending and commonly assigned U.S. Ser. No. 12/984,030 that was filed by Nair, Jennings, Jones, and Sedita, Ser. No. 12/984,044 that was filed by Nair, Jones, and Kapp, and Ser. No. 12/984,055 that was filed by Nair, Jennings, Jones, Sedita, and Olm, all on Jan. 4, 2011, describe porous particles that contain two or more different markers in discrete pores and various uses and methods of preparation. Such porous particles have various utilities including authentication, security (anti-counterfeiting), and electrophotographic purposes as described above.
While the noted porous particles represent an important advance in the art, there is a desire for improved porous particles that have increased resistance to organic solvents, high temperatures, and pressure.